This invention relates to an adaptor for power transmission in a pulley and shaft which is particularly advantageous for adapting a plastic pulley for attachment to a metal shaft for the transmission of power at high torque.
Typically, chain driven pulleys for power transmission are formed of metal and are keyed directly to metal shafts. Alternatively, they may be attached to tapered bushings, also formed of metal, that include a cylindrical aperture and a keyway for connection to the shaft. The tapered bushings have a slightly tapered frustrum that is slit axially along a side to allow the frustrum to compressibly form a strong interference fit with a hole through the pulley. The pulley is further held to the tapered bushing by bolting the pulley to threaded holes in a corresponding flange of the bushing.
Although such metal pulley and shaft systems are well suited to transmitting power at high torque, such systems have well known disadvantages in that they are relatively costly, have heavy rotating parts, can be noisy, and are susceptible to corrosion. For this reason, power transmission components made from plastic are also available. Such components provide for less cost, weight and noise, and greater corrosion resistance; however, they are less able to transmit power at high torque. Where keyed directly to a shaft, the plastic deforms at the keyway under large loads. Moreover, plastic pulleys typically cannot be reliably attached to tapered bushings, because they cannot compress the frustrum sufficiently to form a strong interference fit.
Generally, it is advantageous to provide a pulley and adaptor profile that serves as a guide as well as provides friction surfaces for transmitting torque, as suggested by Draebel, U.S. Pat. No. 5,061,225. A disadvantage of the trapezoidal profiles of Draebal, however, is that such complex profiles are non-standard features in typical pulleys.
Accordingly, there is a need for an adaptor for power transmission in a pulley and shaft that provides for the advantages of light weight, low cost and low acoustical noise available from plastic pulleys and provides for high torque power transmission.